This is a prospective study of the role of genetic and social factors, and their covariation and interaction, in the development and persistence of patterns of alcohol use and abuse, and associated behavioral, health and social problems. 7-year prospective follow-up data are currently being obtained by mailed questionnaire ('1988 survey'), on a clinically unselected sample of 2,800 adult pairs of monozygotic and dizygotic twins from the Australian twin register. Detailed information about drinking style, personality, general morbidity, educational and occupational achievement and family structure are available on these twins from an earlier 1981 survey. We are seeking funding for (i} a more detailed follow-up, by face-to-face to interview, of an enriched sample of pairs where at least one twin is a probable alcohol abuser (N=400 pairs) and a random sample of pairs (N=400 pairs); (ii) a survey by mailed questionnaire (identical to the 1988 questionnaire) of a new cohort of 1,300 pairs of twins aged 18-25 from the Australian register; (iii) a similar mailed survey of 10,000 of the parents, spouses, siblings and parents-in-law of both 1981 and new samples of twins. Structural equation models will be fitted to these data, to resolve the contributions to persistence and change in patterns of alcohol use and abuse of (a) genetic differences; (b) social interaction between family members (including the effects of parents on their children; children on their parents; siblings on each other; spouses on one another; extra-familial environmental influences shared by twins or siblings); (c) changes in the individual's social environment (leaving home; marriage/cohabitation; separation/ divorce/bereavement); (d) self-selection into adverse environments, including genotype-environment correlation, assortative mating and assortative friendship; (e) the interaction of genetic and social factors with sex, age-cohort or salient features of the individual's social environment (e.g. presence or absence of social support). Hypotheses about the etiologic heterogeneity of alcohol abuse will be tested, particularly regarding the differential associations of type I and type II abuse with Harm Avoidance, Reward Dependence and Novelty Seeking personality dimensions.